THE EFFECTS OF ALDEHYDE FIXATION ON ACID PHOSPHATASE ACTIVITY IN TISSUE BLOCKS

The effect of various aldehydes on phosphatase(s) of rat liver and kidney hydrolyzing the monophosphates of β-glycerol, phenol, p-nitrophenol and naphthol AS-TR at pH 5.0 was determined. Biochemical data were correlated with histochemical staining results. On the basis of enzyme recovery after fixation, the aldehydes could be divided into 3 broad groups: (1) well over 50 per cent after hydroxyadipaldehyde and glyoxal; (2) near 50 per cent after formaldehyde and methacrolein; and (3) well below 50 per cent after crotonaldehyde, glutaraldehyde, and acrolein. Acid phosphatase(s) hydrolyzing all 4 substrates showed a similar differential response to fixation by 4 aldehydes, but individual recovery values with naphthol AS-TR phosphate were distinctly lower. Tissues immersed in the first aldehyde group were soft, showed poor morphologic preservation, and a large percentage of the activity was in a soluble state; these features were reflected in the histochemical demonstration of acid phosphatase by an intense staining reaction which was judged to be unsatisfactory. The reverse held true for tissues fixed in aldehydes of the third group, using glutaraldehyde in the staining tests Evidence is presented suggesting that acid phosphatase staining results after formaldehyde fixation is dependent in part on the duration of fixation.